The invention relates generally to positioning underwater devices and, more particularly, to using satellite navigation antennas above the water on a floating body to position devices suspended underwater from the floating body.
The Global Positioning System (GPS) and other satellite navigation systems are used to determine the location of a GPS receiving antenna with a high degree of accuracy. But the signals transmitted by the GPS satellites do not penetrate sea water. So, it is not feasible to position a GPS antenna underwater to determine its location. An underwater device suspended beneath a floating body, such as a buoy, is subject to the rolling, pitching, and rotating that a floating body at the ocean's surface undergoes. Present techniques used to determine the complex motion of a buoy include a four-antenna GPS system and a combination of GPS, compass, and tiltmeters to resolve the buoy's attitude and relate the position of the GPS antenna to an underwater device. But mounting all this equipment to a buoy is complicated and expensive. Furthermore, the power requirements for so many sensors or GPS receivers can be quite high.
Thus, there is a need for a relatively inexpensive and simple way to accurately locate devices suspended underwater from a body floating at the ocean's surface.